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Field Comparison of Dinitrogen Fixation Determined with Nitrogen-15-Depleted and Nitrogen-15-Enriched Ammonium Sulfate in Selected Inbred Backcross Lines of Common Bean

Dep. of Vegetable Crops, Univ. of Florida, Gainesville, FL 32611
Dep. of Horticulture, Rutgers Univ., New Brunswick, NJ 08903
Biology Dep., Albion College, Albion, MI 49224
Dep. of Biochemistry
Dep. of Horticulture, Univ. of Wisconsin-Madison, Madison, WI 53706

^* Corresponding author.

The field determination of N₂ fixation by ¹⁵N-isotopic methods provides a direct and precise measure of N₂ fixation. Since ¹⁵N-enriched fertilizers are expensive, ¹⁵N-depleted (NH₄)₂SO₄ was used as a more economical, readily available alternative to determine N₂ fixation in common bean, Phaseolus vulgaris L. The objectives of this study were to determine whether ¹⁵N-depleted (NH₄)₂SO₄ provided reliable estimates of relative differences in N₂ fixation among bean lines comparable to those obtained using ¹⁵N-enriched (NH₄)₂SO₄, and whether nine previously selected progeny lines differed from their respective recurrent parents for N₂ fixation ability. The nine progeny lines and three parents were grown in two randomized complete block field experiments that were treated identically except that each experiment received only one of the two ¹⁵N fertilizers. Lines were harvested at an early reproductive stage (R3) and maturity (R9), partitioned into plant parts, and the ¹⁵N and total N yield of the tissue determined. The two ¹⁵N fertilizers produced comparable differences among lines at the R9 stage based on significant genotypic rank correlations between the two experiments, and similar fertilizer use efficiency values (% FUE). Three of the five selected progeny lines from population 24 fixed significantly more N₂ than their recurrent parent ‘Sanilac’. The four progeny lines from population 21 were not significantly different from or less effective in N₂ fixation than their recurrent parent ‘Porrillo Sintetico’, therefore, either previous selection based on indirect measures of N₂ fixation was not effective, or the two parents did not differ genetically for N₂ fixation. In all progeny and parental lines, seed N₂ fixed was positively rank correlated with plant N₂ fixed, and the highest N₂- fixing lines in both populations had more fixed N₂ in the seeds than did low N₂-fixing lines.

Received for publication September 9, 1987.